In general, there are many different medical and therapeutic applications in which heat is applied to the body. For instance, heat is applied to increase the body temperature when a person suffers from hypothermia. Heat is also applied to the body to establish certain temperature effects as they are known in the field of physical therapy and medicine (See for instance, U.S. Pat. No. 5,891,187 to Winthrop et al.).
Recently, photodynamic therapy (PDT) has become popular and encompasses a range of treatments that involve a combination of light and a photo-active chemical agent. This light-activated drug is administered or applied to the patient, followed by illumination with intense light of a specific wavelength matched to the photo-sensitive qualities of the drug. Interaction between the drug and light causes destruction of the target tumor or lesion. Typically, a laser is used as the light source, however, other types of intense light sources may be used in certain dermatological applications.
In U.S. Pat. No. 4,891,043, Zeimer et al. teaches in an application related to PDT that it is necessary for his application to increase the temperature in a particular anatomical locus to approximately 41 degrees Celsius to locally release the content of the liposomes. Zeimer et al. teaches the use of encapsulating drugs inside a liposome, which are not broken unless heated to approximately 41 degrees Celsius. Zeimer et al. teaches that the temperature is accomplished by irradiating the laser light absorbing liposomes at the specific site via a laser beam. Furthermore, Zeimer et al. teaches that it is advantageous to use a argon or krypton laser capable of delivering laser beam pulses with each pulse having a duration of about 200 to about 500 ms.
In U.S. Pat. No. 6,248,727 Zeimer further teaches a first laser beam to selectively heat tissue, including its blood vessels or sinuses, to a temperature of approximately 41 degrees Celcius without causing substantial physiological damage to that tissue or vasculature. A second laser beam is then used to suitably activate a tissue-reactive agent without causing substantial physiological damage to the vasculature in which it is disposed.
In U.S. Pat. No. 5,225,433 Dougherty et al. teaches a treatment in which a photosensitizing drug is injected into a subject. In treating humans or other mammals with the drug, light is irradiated on the tissue in such a position as to uniformly illuminate cancer tissue. Dougherty et al. then further teaches that heat is applied in the range of 40.5 to 45 degrees Celcius. The increase in temperature, accordingly to Dougherty et al., may be achieved by transmitting light: (1) some of which is near or in the infrared spectrum such as at 1060 nm wavelength from a Nd-Yag laser for heat with the light at 630 nm for interaction with the photosensitive drug; or (2) by microwaves such as the 2450 Mhz; or (3) by any other suitable means.
However, in any application where heat is applied to biological tissue during a medical or therapeutic application, irreversible damage to the tissue due to heating, unless intended, should be avoided. Therefore, it is imperative to have feedback from the target area over the temperature. A lack of any type of feedback makes current heating techniques less desirable and difficult to accept in practice. Accordingly, there is a need for advanced heating devices and methods that can be safely used for therapeutic or medical applications.